Although several conserved signaling pathways such as IGF-1, AC-PKA, Ras/Raf/MAPkinase, TOR- S6K and Sir2 are known to regulate stress resistance and longevity in various organisms, the mechanism by which the RGS (regulator of G-protein signaling) protein affects the aging process through the G-protein signaling pathway is not understood yet. Our preliminary data exhibited that 1) reduced expression of a RGS protein, Loco, resulted in a longer lifespan of flies, with stronger resistances to stressors, higher MnSOD activity, and increased fat content. 2) In contrast, overexpression of the loco gene shortened lifespan significantly with lower stress resistance and reduced fat content, also indicating that is RGS domain is related to the regulation of longevity. 3) Interestingly, the expressional changes of yeast RGS2 and rat RGS14, homologues of the fly Loco, also affected oxidative stress resistance and longevity in the respective species, suggesting that the Loco/RGS14 signaling pathway is evolutionarily conserved in various organisms for the regulation of longevity. It is known that fly Loco increases adenylate cyclase (AC) activity by inactivating the inhibitory GiGTP protein and that mammalian RGS14 interacts with activated H-Ras and Raf-1 kinases, which subsequently inhibit ERK phosphorylation. Corroboratively, our preliminary data showed that downregulation of Loco significantly diminishes cAMP amounts and increases p-ERK levels with higher resistance to oxidative stress. In addition, our proteomic iTRAQ and Phos-tag gel analyses revealed that reduction of Loco signaling decreases phosphorylation levels of the Rpd3 protein (HDAC1, histone deacetylase 1), which may be regulated by p-ERK in the Loco pathway. Reduced expression of Rpd3 is reported to extend the lifespan in Drosophila. However, the way in which Rpd3/HDAC1 activity is regulated for the longevity mechanism is not characterized. We also found that fat body-specific downregulation of the loco gene enhances stress resistance and longevity. Based on our preliminary data, the specific hypothesis for this research is that the Loco/RGS14, a RGS protein, regulates stress resistance and longevity by modulating the phosphorylation level of Rpd3/HDAC1 protein in a tissue (fat body)- specific manner. The specific aims are to examine I) if Loco signaling modulates Rpd3 activity through phosphorylation of Rpd3 S419/S421 sites identified from unbiased iTRAQ screening, and II) if change of the phospho-Rpd3/HDAC1 level in Loco/RGS14 signaling determines stress resistance and lifespan through the target genes of histone deacetylase Rpd3. Our research will explore new aging field to determine how the G- protein signaling pathway (Loco) epigenetically regulates the chromatin remodeling complex (Rpd3) during aging process.